P. Griess (Ber., 1872, 5, p. 192; 18 74, 7, p. 1223) orientated the three diaminobenzenes or phenylene diamines by considering their preparation by the elimination of the carboxyl group in the six diaminobenzoic acids.
Thus ortho-phenylene diamine yields the following products: N H N ./`N; Xn NZ In some cases oxidation of condensed benzenoid-heterocyclic nuclei results in the rupture of the heterocyclic ring with the formation of a benzene dicarboxylic acid; but if the aromatic nucleus be weakened by the introduction of an amino group, then it is the benzenoid nucleus which is destroyed and a dicarboxylic acid of the heterocyclic ring system obtained.
The para or true quinones are obtained by the oxidation of hydrocarbons with chromic acid or of various para di-derivatives of benzene with chromic acid mixture, such, for example, as para-aminophenol, para-phenylene diamine, paraa.minoazobenzene, &c. H.
Witt (Ber., 1877, 10, p. 656), is obtained by coupling phenyl diazonium chloride with meta-phenylene diamine.
Triamino-azo-benzene: (meta-aminobenzene-azo-meta-phenylene diamine or Bismarck brown, phenylene brown, vesuvine, Manchester brown), NH 2.
Acid on meta-phenylene diamine.
It forms practically colourless needles which melt at 89.7° C., and boil at 302.8° C. It is used for the preparation of meta-phenylene diamine.
The Skraup reaction is a perfectly general one for primary amino-compounds; the halogen-, nitroand oxy-anilines (aminophenols) react similarly, as do also the toluidines, naphthylamines, aminoanthracene, metaand para-phenylene diamines, and orthoand 7-aminoquinoline.
It may be prepared synthetically by fusing meta-iodophenol, phenol meta-sulphonic acid, and benzene meta-disulphonic acid with potash; by the action of nitrous acid on meta-aminophenol; or by the action of 10% hydrochloric acid on meta-phenylene diamine (J.